(BaseballStL) -- It’s not often that a one-out walk is considered the key moment in a game, but it’s hard not to consider Daniel Descalso’s free pass in the seventh inning as a defining moment in Game 2 on Thursday.

After back-to-back batters reached base and advanced on a double-steal for St. Louis, Descalso fouled off an 82-mph slider from Red Sox reliever Craig Breslow on the sixth pitch of the at-bat. The seventh pitch, an 85-mph slider, ran inside on Descalso for a close ‘ball four’ call.

It was clearly a ball, but close enough to swing at especially with a full count.

The free pass led to bases loaded for Cardinals’ leadoff man Matt Carpenter, who would hit a sacrifice fly to tie the game as a couple errors from catcher Jarrod Saltalamacchia and Breslow led to another run for a 3-2 St. Louis lead. Carlos Beltran singled Descalso home from third base for a 4-2 lead in the seventh.

“The (first) walk starts to get things going for them,” Red Sox manager John Farrell said. “After the base hit to Jay, felt like we were in a pretty good situation for a matchup. And then unfortunately the walk and the errant throw, that's the one in looking back. I'm sure Craig (Breslow) would like to have that ball back and hold it with a chance to shut down the inning right there. We give them the run.”

Back to Descalso’s walk -- the pitch could have gone a variety of ways had the shortstop swung at it.

A swing-and-miss would have resulted in the second out. Carpenter’s fly out would have been the final out of the inning instead of a game-tying sacrifice fly.

A foul tip would have brought another pitch which could have been anything, but we’ll never know.

It was also close enough that home plate umpire Mark Wegner could have called it strike No. 3, although it would have brought a huge fuss from the Cardinals dugout. There was no controversy of whether it was a ball.

It was the gutsy decision of Descalso not to swing that led to a three-run seventh inning, and a 4-2 Cardinals win.